Denervation, long-term anesthesia of the motor nerve, treatment of the motor nerve with colchicine and, to a certain extent, muscle paralysis by spinal cord transection all produce supersensitivity to ACh of the muscle membrane. A decrease in the electric conductance of muscle membranes has also been found after denervation, but not after colchicine treatment of the nerve. Since nerve and muscle activity continues after colchicine treatment but not after denervation, the result suggested that the change in the muscle membrane ionic conductance depends on muscle activity. On the previous research in which some questions regarding the measurement of ionic conductances were clarified, membrane conductance measurements will be made in muscles which have become supersensitive to ACh by treating the nerve in the ways mentioned and in muscles which have been immobilized, tenotomized, or inactivated by spinal cord section. The results are expected to throw some light on the interrelationship between ACh supersensitivity and membrane ionic conductance changes in muscle. BIBLIOGRAPHIC REFERENCES: H. Lorkovic, W.M. Hooker, and R.J. Tomanek. Localization of the acetylcholine receptors in denervated muscles of rats. Arch. Internat. Physiol. Bioch. 83, 493-504, 1975. Lorkovic, H. Voltage-current relationships and voltage oscillations in Cl-free washed rat muscles. Federation Proc. (l976) in press.